In the tobacco industry, when considering, for example, groups of packets of cigarettes, units for transferring groups of packets of cigarettes are known, which comprise a transfer member for engaging a conveying path traveled by the groups, and an actuating device for moving and imparting to the transfer member a given trajectory having a forward portion in common with the conveying path. The actuating device normally comprises a main arm rotating with respect to the conveying path of the groups; a secondary arm fitted in rotary manner to the main arm to support the transfer member; and a two-stage epicyclic gear train having a first stage associated with the main arm to mainly impart a given orientation to the transfer member, and a second stage associated with the secondary arm to rotate the secondary arm with respect to the main arm and impart a given-shaped trajectory to the transfer member.
More specifically, in operating units of the above type, the second stage of the actuating device comprises two gears meshing with each other and having a constant transmission ratio determining the shape of the trajectory, which may be elliptical with any predetermined elongation ratio, triangular, square or circular.
The major drawback of known operating units of the above type lies in the fact that such units are very "rigid" in the sense that any given transmission ratio corresponds to a specific trajectory of the transfer member and a specific law of motion (velocity, acceleration, etc.) of the transfer member along such trajectory.